How does a rattlesnake rattle?
It’s easy to recognize a rattlesnake by the rattle at the end of its tail. The rattle is a series of horny, cup-shaped rings that fit loosely into one another. When a rattlesnake rattles, it is usually because it has become alarmed.
This makes it vibrate its tail rapidly. The hollow rings strike together and make a sharp buzzing sound.
By making its rattling noises, the rattlesnake is able to warn away bigger animals that might step on it or harm it. Although a rattlesnake often gives a warning before it strikes it may also strike without rattling.–Dick Rogers